Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a leading cause of life-threatening infections in the United States and is now responsible for more deaths annually than HIV/AIDS. Even worse, nine epidemiologically unrelated cases involving the transfer of vancomycin resistance genes from enterococci to MRSA have recently been documented in the U.S., raising the frightening possibility that vancomycin, long known as the "drug of last resort" for the treatment of MRSA infections, will become ineffective in the next few years. Resistance to newer anti-MRSA antibiotics has already been observed. This Program Project Grant was motivated by the urgent need to understand the development and spread of antibiotic resistance in S. aureus, and to explore novel compounds and strategies to treat MRSA infections. In our proposal, we outline three projects that are directed towards addressing the need to explore new approaches to treat S. aureus infections. The first project is aimed at exploring the utility of chemoenzymatic approaches for the synthesis of phosphoglycolipid analogs (PGLs). PGLs are potent, structurally novel natural products that inhibit an unexploited target in a well-validated pathway for antibiotics, peptidoglycan biosynthesis. These features of PGLs make them promising antibiotic leads, but it has not been possible to explore their potential because there have been no efficient strategies developed to make analogs. Hence, our primary goal with this project is to establish feasible methods to make analogs. The goals of the second project are two-fold: 1) to identify the specific target of an anti-staphylococal small molecule antibiotic we have discovered that inhibits wall teichoic acid (WTA) biosynthesis; and 2) to use the compound to assess whether the WTA pathway is a robust antibiotic target. The goals of the third project are to test a hypothesis about a novel strategy to restore methicillin sensitivity to MRSA strains and to establish a screen to identify small molecules that render MRSA susceptible to methicillin. Synergies with the Pis of other subprojects will enable us to evaluate compounds and assess the development of resistance in animal models. The proposed research could lead to new approaches to treating S. aureus infections, including MRSA infections. RELEVANCE (See instructions): Resistance to existing antibiotics has become a major problem in hospitals and is increasingly common in the community. We need new antibiotics to treat methicillin-resistant S. aureus infections. This proposed research is directed towards exploring new compounds and strategies to treat MRSA infections.